Environmental and economic concerns are forcing agricultural procedures to modify traditional practices to remain viable. Soil conservation, moisture conservation, and herbicide costs are the primary concerns facing the North American agricultural producer.
In most dry land farming the crops are moisture limited so that a field must be rotated, using a fallow year. The traditional practice in fallow is to use tillage to control the weeds. However in dry land conditions the use of tillage promotes moisture loss ad soil erosion. Leaving the field to stubble reduces the moisture loss and soil erosion. The stubble is useful in trapping snow during the winter, reduces the evaporation during the summer, and fixes the soil to reduce erosion.
Chemical fallow procedures use herbicides to control the weeds in stubble. Traditionally chemical weed control procedures for land in fallow require the applicator to spray the entire field. Broadcast spraying of herbicide for weed control is more expensive, in the short term, than tillage.
There is a need to detect weeds in fallow or stubble fields so that the weeds can be selectively sprayed without spraying the entire field. Current general usage does not follow this procedure. However the present invention allows the applicator to selectively spray weeds in stubble or fallow, thus reducing the cost of chemically controlled fallow.
A prior art selective sprayer product sold under the trademark Detect-Spray by an Australian company is described in U.S. Pat. No. 5,144,767.
The Detect-Spray system uses 2 narrow-band optical filters, in the near infrared and red ranges, to identify weeds. It also uses a centralized controller and is cabled using a star configuration. Identification of weeds is effected by measuring irradiance and radiance values within the field-of-view in the near infra red and red portions of the spectrum. Reflectance values in each spectrum portion are then calculated. The ratio of the two reflectance values so obtained is then used to identify if weeds (meaning predominantly green, chlorophyll-containing vegetation) are present within the field-of-view. Unfortunately, chlorophyll can be present in both "active" and "inactive" modes, and the sensitivity of this system is reduced when chlorophyll is in its inactive mode.
Another prior art reference is the Spot Shot (TM) system which uses an "electric eye" to detect any plant that is taller than a set height. The Spot Shot turns on a solenoid whenever a tall plant, presumed to be a weed, interrupts the light beam. The Spot Shot system does not detect ground hugging weeds, and generally will not work satisfactorily in standing stubble because the straw interrupts the beam.
The present invention has as its objective the provision of an improved means for identifying weeds in fallow or stubble fields, whereby weed-control chemicals may be selectively applied to such weeds.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.